The present invention is directed to ink compositions. More specifically, the present invention is directed to ink compositions particularly suitable for use in thermal ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises an aqueous phase, an oil phase, an oil-soluble dye, and a surfactant, said ink exhibiting a liquid crystalline gel phase at a first temperature and a liquid microemulsion phase at a second temperature higher than the first temperature.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink, in excess of the normal boiling point, diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be retired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224, and U.S. Patent 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Ink jet printing processes may also employ inks that are solid at room temperature and liquid at elevated temperatures. For example, U.S. Pat. No. 4,490,731, the disclosure of which is totally incorporated herein by reference, discloses an apparatus for dispensing solid ink for printing on a substrate such as paper. The ink dye vehicle is chosen to have a melting point above room temperature, so that the ink which is melted in the apparatus will not be subject to evaporation or spillage during periods of nonprinting. The vehicle is also chosen to have a low critical temperature to permit the use of the solid ink in a thermal ink jet printer. In thermal ink jet printing processes employing hot melt inks, the solid ink is melted by a heater in the printing apparatus and utilized as a liquid in a manner similar to that of conventional thermal ink jet printing. Upon contact with the printing substrate, the molten ink solidifies rapidly, enabling the dye to remain on the surface instead of being carried into the paper by capillary action, thereby enabling higher print density than is generally obtained with liquid inks. Advantages of a hot melt ink in ink jet printing are elimination of potential spillage of the ink during handling, a wide range of print density and quality, minimal paper cockle or distortion, and enablement of indefinite periods of nonprinting without the danger of nozzle clogging, even without capping the nozzles.
In addition, U.S. Pat. No. 4,751,528, the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink jet system which includes a temperature-controlled platen provided with a heater and a thermoelectric cooler electrically connected to a heat pump and a temperature control unit for controlling the operation of the heater and the heat pump to maintain the platen temperature at a desired level. The apparatus also includes a second thermoelectric cooler to solidify hot melt ink in a selected zone more rapidly to avoid offset by a pinch roll coming in contact with the surface of the substrate to which hot melt ink has been applied. An airtight enclosure surrounding the platen is connected to a vacuum pump and has slits adjacent to the platen to hold the substrate in thermal contact with the platen.
Further, U.S. Pat. No. 4,791,439, the disclosure of which is totally incorporated by reference, discloses an apparatus for use with hot melt inks having an integrally connected ink jet head and reservoir system, the reservoir system including a highly efficient heat conducting plate inserted within an essentially non-heat conducting reservoir housing. The reservoir system has a sloping flow path between an inlet position and a sump from which ink is drawn to the head, and includes a plurality of vanes situated upon the plate for rapid heat transfer.
Ink compositions for ink jet printing are known. For example, U.S. Pat. No. 4,840,674 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises a major amount of water, an organic solvent selected from the group consisting of tetramethylene sulfone, 1,1,3,3-tetramethyl urea, 3-methyl sulfolane, and 1,3-dimethyl-2-imidazolidone, which solvent has permanently dissolved therein spirit soluble dyes.
U.S. Pat. No. 5,006,170 (Schwarz) and U.S. Pat. No. 5,122,187 (Marchessault et al.), the disclosures of each of which are totally incorporated herein by reference, disclose hot melt ink compositions suitable for ink jet printing which comprise a colorant, a binder, and a propellant selected from the group consisting of hydrazinc; cyclic amines; ureas; carboxylic acids; sulfonic acids; aldehydes; ketones; hydrocarbons; esters; phenols; amides; iraides; halocarbons; urethanes; ethers; sulfones; sulfamides; sulfonamides; phosphites; phosphonates; phosphates; alkyl sulfides; alkyl acetates; and sulfur dioxide. Also disclosed are hot melt ink compositions suitable for ink jet printing which comprise a colorant, a propellant, and a binder selected from the group consisting of rosin esters; polyamides; dimer acid amides; fatty acid amides; epoxy resins; fluid paraffin waxes; fluid microcrystalline waxes; Fischer-Tropsch waxes; polyvinyl alcohol resins; polyols; cellulose esters; cellulose ethers; polyvinyl pyridine resins; fatty acids; fatty acid esters; poly sulfonamides; benzoate esters; long chain alcohols; phthalate plasticizers; citrate plasticizers; maleate plasticizers; sulfones; polyvinyl pyrrolidinone copolymers; polyvinyl pyrrolidone/polyvinyl acetate copolymers; novalac resins; natural product waxes; mixtures of linear primary alcohols and linear long chain amides; and mixtures of linear primary alcohols and fatty acid amides. In one embodiment, the binder comprises a liquid crystalline material.
U.S. Pat. No. 5,021,802 (Allred), the disclosure of which is totally incorporated herein by reference, discloses a bubble jet ink which comprises 90 to 99.9 percent by weight of aqueous sol-gel medium and 0.1 to 1 percent by weight colorant. The inks are thermally reversible sol-gels which are gels at ambient temperatures and form liquid sols at temperatures between about 40.degree. and 100.degree. C.
U.S. Pat. No. 5,041,161 (Cooke et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink which is semi-solid at room temperature. The ink combines the advantageous properties of thermal phase change inks and liquid inks. The inks comprise vehicles, such as glyceryl esters, polyoxyethylene esters, waxes, fatty acids, and mixtures thereof, which are semi-solid at temperatures between 20.degree. and 45.degree. C. The ink is impulse jetted at an elevated temperature in the range of above 45.degree. C. to about 110.degree. C., at which temperature the ink has a viscosity of about 10 to 15 centipoise. The inks also contain 0.1 to 30 weight percent of a colorant system.
U.S. Pat. Nos. 4,853,036 and 5,124,718 disclose an ink for ink jet recording which comprises a liquid composition essentially comprising a coloring matter, a volatile solvent having a vapor pressure of 1 mm Hg or more at 25.degree. C., and a material being solid at room temperature and having a molecular weight of 300 or more, and prepared so as to satisfy the formula B.sub.1 /A.sub.1 .gtoreq.3, assuming viscosity as A1 cP at 25.degree. C., measured when the content of the solid material in the composition is 10 percent by weight, and assuming viscosity as B.sub.1 cP at 25.degree. C., measured when the content of the solid material in the composition is 30 percent by weight. An ink jet recording process using the ink is also disclosed.
U.S. Pat. No. 5,065,167 (You et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink including a waxy carrier that is solid at 25.degree. C. and liquid at the operating temperature of an ink jet nozzle and a driver having a critical pressure greater than 10 atmospheres, the carrier and driver being miscible in liquid phase.
U.S. Pat. No. 5,047,084 (Miller et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink in the form of a microemulsion of an organic vehicle phase comprising fatty acid and colorant dispersed therein and an aqueous phase containing a surfactant, the vehicle phase preferably being liquid at 70.degree. C. and solid at 20.degree. C.
U.S. Pat. No. 5,226,957 (Wickramanayake et al.), the disclosure of which is totally incorporated herein by reference, discloses water insoluble dyes formulated in a microemulsion-based ink which is waterfast, non-threading, and bleed-alleviated. The inks comprise (a) about 0.05 to 0.75 weight percent of a high molecular weight colloid, (b) about 0.1 to 40 weight percent of at least two surfactants, comprising at least one surfactant and at least one co-surfactant, (c) about 0.5 to 20 weight percent of at least one cosolvent, (d) about 0.1 to 5 weight percent of at least one water insoluble dye, (e) about 0.1 to 20 weight percent of an oil, and (f) the balance water. The ink forms a stable microemulsion.
"Stabilization of Inverse Micelles by Nonionic Surfactants," Stig E. Friberg, contained in Interfacial Phenomena in Apolar Media, Eicke & Parfitt, eds., Marcel Dekker Inc. (New York and Basel 1987), the disclosure of which is totally incorporated herein by reference, discloses and describes systems with hydrocarbon, water, and nonionic polyalkylene glycol alkyl ether surfactants which display pronounced variation of their phase patterns with temperature. At particular temperatures and component concentrations, a lamellar liquid crystalline phase is observed.
"A Hot Melt Ink for Thermal Jet Printing," A. H. Sporer et al., Journal of Imaging Science and Technology, Vol. 36, No. 2, p. 176 (March/April 1992), the disclosure of which is totally incorporated herein by reference, discloses an ink technology wherein the fluid vehicle of the ink is a stable, single-phase, water-in-oil (wax) microemulsion at elevated temperatures in the range of 70.degree. to 95.degree. C., yet is a solid at ambient temperatures. The ink, because it is a microemulsion, is stable to freeze-melt cycles. The ink is suitable for jetting as a hot melt ink in conventional continuous or impulse ink jet apparatus, and can also operate in impulse thermal ink jet printheads where other hot melt ink jet ink compositions cannot.
Copending Application entitled "Coated Recording Sheets," with the named inventor William M. Schwarz, the disclosure of which is totally incorporated herein by reference, discloses a recording sheet which comprises a substrate and a coating thereon comprising water and a surfactant capable of exhibiting a liquid crystalline phase in water at a temperature of about 25.degree. C. or higher, said coating containing the water and surfactant in relative concentrations such that upon addition of water to the coating, the surfactant undergoes a phase change, thereby increasing the viscosity of the coating. In one embodiment, the surfactant is in a lamellar liquid crystalline phase and, upon addition of water to the coating, the surfactant undergoes a phase change to a hexagonal liquid crystalline phase. Also disclosed are ink jet printing processes wherein an aqueous ink is applied to the aforementioned recording sheet.
While known compositions and processes are suitable for their intended purposes, a need remains for ink compositions suitable for thermal ink jet printing. In addition, there is a need for ink compositions which are compatible with a wide variety of plain papers. Further, a need exists for ink compositions compatible with a wide variety of plain papers without the need for special ink drying hardware in the printing apparatus. Additionally, there is a need for ink compositions which generate high quality, waterfast images on plain papers. There is also a need for thermal ink jet ink compositions which generate high quality, fast-drying images on a wide variety of plain papers at low cost, with high quality text, high quality graphics, minimal feathering, minimal intercolor bleed, and excellent image permance. Further, there is a need for thermal ink jet ink compositions which can be employed without the need for very high printhead temperatures.